Numerical micromagnetics in hard magnetic and multilayer systems (invited)

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Abstract
Micromagnetic finite element calculations using a magnetic vector potential to treat long-range dipolar interactions describe the interactive magnetization processes which determine the magnetic properties of fine-grained magnetic materials. Micromagnetic models give a quantitative treatment of the correlation between the microstructure and the magnetic properties of melt-spun Nd2Fe14B magnets and of Co/Pt multilayers. In nanocrystalline permanent magnets, intergrain exchange interactions cause nonuniform magnetic states which increase the remanence and act as nucleation sites. Remanence increases with decreasing grain size. Remanence enhancement of about 15% with respect to noninteracting particles can be achieved for an average grain size D≤20 nm. On the other hand, the nucleation field reduces to about 20% of the anisotropy field. Once a reversed domain has been nucleated, strong internal stray fields cause the expansion of the domain over several grains. The nucleation field of Co/Pt multilayers increases with improving texture. Spatial fluctuations of the magnetocrystalline anisotropy energy create barriers for domain wall motion. The pinning field of reversed domains increases with increasing misalignment and with increasing grain size. The quality of texture and the grain size significantly influence the jaggedness of domains in Co/Pt multilayers. Large grains and strong deviations of the easy directions from the film normal deteriorate the smoothness of domains and increase the transition width.

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